Dell Precision has been their best line... both desktop and laptop. Dell Dimension, originally their "middle" grade but now discontinued, has been very good too. The 1st one I had was sold to a neighbor, and he still uses it daily... going on 15(?) years old.
Yes, They are good. I do know though that they are living on borrowed time, but so am I for that matter!! Dell's 8900 series looks like a good replacement for Dimension.
That's "XPS 8900", right? If so, I'm not a fan. Haven't looked at them lately, but last time I did they had a "lesser" motherboard. My view is that the XPS line is marketed as something better than it actually is.... same with OptiPlex line. My recommendation is Dell Precision... off of their Outlet site to save some $$ or used... both desktop and laptop. Seems Dell's "2nd best" line of laptops.... Latitude... might be good also. (Less confidence all around in laptops. Nearly all are made by just 5 companies in Asia and rebadged. Hard to tell exactly what you're getting in a mobo.) I don't think Dell has an adequate replacement for the Dimension line. They abandoned the "middle grade" concept some years back and have since gone with "workstation class" (Precision) and various "consumer" lines. (Not sure what to think about Alienware... except it's high priced.)
Most of the reviews (probably written by Dell!) I've read about XPS have been good. But, of course, not written by those who trade. Do you mean the 3000 Precision series or the 5000? The 3000 CPU is only i5 and can't upgrade. And 5000's CPU is Xeon, and 80% more expensive than XPS8900. These specs may be different from where you are. Anyway, as you suggested, I'll look into Precision when the time comes.
Whichever Precision suits your needs. If I were buying one today, I'd look for a deal on the Precision T5810. Decent deals on those with Xeon E5-1620 CPU run about $850. I've seen deals on it ~$650 two different times. I view the T5810 at this price to be a benchmark comparison for value, quality, performance. From their Outlet website, comes with same 3-yr warranty as new.
I've had 10+ years of happiness with bog standard Dell machines, just make sure they have a decent chip (i3/i5) and 8GB Ram and you'll be fine for most PC jobs. I always think of them as like Ford tractors, the brand will never win any prizes but they do the job well.
I must have a black thumb on keeping equipment running, displays goes out, some overheat-although all of them stay on running backtesting, since I been changing them out regularly, much less problems. Laptop I use for email, in January the CPU kept maxing out even after clean install of Windows 7 at idle, had to put on Windows 10, now CPU is at 20%. I make backups and never fails when I need the backup, doesn't work. And I donate to area schools, so they don't get tossed out. If you know how to trade, don't need anything fancy, 8-16 Ram and anything faster than cell phone connection, although I have day traded with that.
Few minutes ago, I got an email ad from Dell for a T5810, Xeon E5-1620 CPU, 8GB RAM, etc... for $906. Not the best price ever, but not terrible either.